1. Field of the Invention
The present invention relates to drive reversing mechanisms for harvesting machines such as combine harvesters. More particularly the invention relates to mechanisms for reversing the drive of a component of such machines for removing a lump of crop material which has caused a blockage in the machine.
2. Description of the Prior Art
It occasionally happens in combine harvesters that the threshing cylinder or the straw elevator becomes blocked by an excess of crop material being fed between the threshing cylinder and the threshing concave, and between the straw elevator chain and the elevator floor, respectively. Much more frequently, the header auger becomes blocked by an excessively large lump of crop material which wedges between the auger flights and the header floor. In all these circumstances either a safety clutch or drive belts start to slip. Clearing a blockage in the threshing means normally can be accomplished merely by lowering the threshing concave and re-engaging the drive, whereby the lump of material will pass through the enlarged gap between the threshing cylinder and threshing concave. Clearing a blockage in the straw elevator is much more difficult and time consuming. Access doors must be opened and the lump must be pulled out manually. Avoiding such blockages obviously would be much more desirable. It is possible to set the safety clutches in the drives of the elevator and the header so that if an excessively large lump of crop material is present, normally a blockage of the header auger will occur rather than of the elevator. Practice indicates that about 95-98% of elevator blockages can be avoided in this way.
However, clearing a blockage of the header auger also must be accomplished manually in most conventional machines. This is also very time consuming, dirty and sometimes difficult. It is indeed sometimes difficult as the blocking lump of material may be held very tightly between the auger and the header floor so that it can be removed only piece by piece. However, time is extremely valuable especially during the short harvesting period and therefore long interruptions in operation such as caused by the clearing of a blocked machine cannot be tolerated. Moreover, clearing a header blockage is a dangerous exercise as the operator normally has to reach the header auger from between the reel and the cutterbar so that he may contact either the reel tines and/or the sharp edges and points of the cutterbar and be injured thereby.
Similar problems of blockages and clearing the same are known also in connection with other agricultural harvesting machines, such as forage harvesters.
In an attempt to overcome the foregoing problems it is common practice on forage harvesters to provide a reversible gearbox in the drive of the feed rolls thereof and of the pick-up attachment. A reversible gearbox in the header drive of a combine harvester is also known as evidenced by the disclosure of Belgian Pat. No. 860.077. However, such reversible gearboxes are relatively expensive as they involve a large number of gears. This extra expense is difficult to justify having regard to the number of times and duration of usage of the reverse drive.
In another prior art arrangement, means have been proposed for driving the threshing cylinder in reverse when the latter is blocked. To this end the threshing cylinder is drivingly coupled by special drive means to one of the traction wheels of the combine and the combine is moved rearwardly to effect the clearing of a blockage. Thus as the combine is driven rearwardly, the blocking lump of material is removed in a forward direction. This is a complicated and expensive approach to the problem and has not proved to be a practicable proposition. Furthermore, the lump of material cleared from the threshing means in this manner can merely be fed back to the elevator so that it again causes a blockage when the combine is driven forward. Such an arrangement shown in German UM No. 69.13.630.
In another arrangement a double declutching device for a combine harvester has been proposed for declutching the traction drive for the forward movement of the machine and the drive to the header simultaneously, or shortly one after the other, with only one control. This is done as soon as a crop feeding problem, for example in the header, is noticed. However in practice it appears that quite often such a feeding problem is noticed too late and that a blockage occurs before the operator has had a chance to intervene. Thus this arrangement is not entirely satisfactory and is of no use once a blockage has occurred as it does not effect any clearance of a blockage. Such an arrangement is shown in German Pat. No. 1,655,576.